The present invention relates to UV curable organopolysiloxane compositions which are convertible to nontoxic, adherent, release coatings when applied onto a paper or a plastic substrate and cured thereon. More particularly, the present invention relates to the use of a compatibilizer, such as a mixture of a C.sub.( 8-2) alkylphenol and an alkanediol, such as butanediol, for facilitating the incorporation of a photoinitiator, such as a polyaryloniumhexafluorometalloid salt, for example, a diaryliodoniumhexafluoroantimonate salt into an epoxysilicone fluid to provide a UV curable silicone composition convertible to a non-toxic release coating
Prior to the present invention, as shown by Eckberg et al U.S. Pat. No. 4,279,717, UV curable epoxysilicone coating compositions were provided by using bisaryliodonium salts such as bis(dodecylphenyl) iodonium salts, in combination with an epoxy functional silicone. As taught by Eckberg et al, the efficiency of the bisaryliodonium photo initiator, was highly dependent upon whether the photoinitiator could be readily dispersed or dissolved into the epoxy functional silicone fluid. Even though the bis(alkylatedphenyl)iodonium salts taught by Eckberg et al have been found to rapidly dissolve in the epoxy silicone fluid, experience has shown that the resulting UV curable epoxysilicone composition often cannot satisfy the rigid toxicity standards required for making adherent silicone release coatings used in food applications.
As taught in the copending application of Crivello, et al, U.S. Ser. No.171,063 filed Mar. 21,1988, now U.S. Pat. No. 4,882,201 for Non-Toxic Arylonium Salts, UV Curable Coating Compositions and Food Packaging Use, the use of certain arylonium salts is described having at least one nuclear bound-OR group attached to the aryl nucleus by a carbon-oxygen linkage, where R is an alkyl radical having at least eight carbon atoms. These arylonium salts exhibit substantially less toxicity than prior art arylonium salts free of such nuclear bound OR groups. Experience has shown however, that although such arylonium salts, for example, diaryliodoniumhexafluoroantimonate salts exhibit reduced toxicity and accordingly satisfy food packaging standards, they have been found to be substantially incompatible with epoxysilicones having less than about 12 mole percent of condensed epoxy organosiloxy units, based on the total moles of diorganosiloxy units in such epoxysilicone. It has been further found that unless the non-toxic arylonium salt is miscible with the epoxysilicone, a heterogenous curable coating mixture can be formed having a tendency to readily smear or streak after being subjected to curing conditions on the surface of a suitable substrate, such as plastic or paper. Improved diaryliodonium salt compatability can be achieved by raising the epoxy mole percent in the expoysilicone. However, as the condensed epoxy content rises in the epoxysilicone, the release characteristics of the cured coating are adversely affected.
It would be desirable therefore to provide nontoxic UV curable silicone coating compositions utilizing epoxysilicone fluid having less than about 12 mole percent of condensed epoxyorganosiloxy units, based on the total moles of condensed diorganosiloxy in such epoxy silicone fluid, and capable of providing non-toxic, non-smearing release coatings on paper or plastic substrates. It also would be desirable to provide substantially uniform UV curable epoxysilicone compositions which do not contain incompatable photoinitiators having a tendency to settle out of the curable mixture upon standing.